1. Field of the Invention
This invention relates to an anti-skid control system for a vehicle, such as an automotive vehicle. This invention also relates to a vehicle speed deducing system usable in a vehicle control system, such as a vehicle anti-skid control system.
2. Description of the Prior Art
In some known vehicle anti-skid control systems, vehicle wheel rotational speed is detected by a sensor and also pseudo vehicle speed is determined by processing the output signal from the vehicle wheel speed sensor. During application of a vehicle brake, the pseudo vehicle speed is compared with the vehicle wheel speed to determine vehicle wheel slip ratio. Brake force applied to vehicle wheels by the brake is adjusted in accordance with the determined slip ratio so that unacceptable degree of vehicle wheel slippage can be prevented and the vehicle can be optimally braked. Japanese published examined patent application No. 59-30585 discloses such a vehicle anti-skid control system.
In other known vehicle anti-skid control systems, vehicle speed used in controlling brake force is deduced from the highest of vehicle wheel rotational speeds detected by a plurality of sensors associated with respective vehicle wheels or deduced from given deceleration. When the vehicle wheels are locked, or when all of the vehicle wheels undergo essentially the same slip ratio, the deduced vehicle speed tends to be lower than the actual vehicle speed. Such a deviation of the deduced vehicle speed from the actual vehicle speed lowers the accuracy or reliability of the anti-skid control.